Cloning and sequencing of cDNA encoding for a novel human testis-specific contraceptive vaccinogen: role in immunocontraception

Immunocontraceptives: How far from reality?

Despite high expectations of safer, effective, economical, longer acting contraceptives, to date, there are no licensed contraceptive vaccines available in the market. Nevertheless, a role for vaccines undoubtedly exists as an aid to birth spacing and as a nonsurgical means of generating sterility. The research concerned in the area so far has been successful on the feline population, with room still for exhaustive studies on humans. The future of contraceptive vaccines holds great promise in terms of comfort, price, efficacy, rare complications, and possibly nonselective action on animal populations as well as on humans. This brief review deals with the basic aspects of immunocontraceptives along with the efforts done so far. There is a need for further research in aspects involving the rate of evolution of contraception resistance based on genetics, resistance phenotypes, or cross generation effects. Gonadotropin-releasing hormone and luteinizing-hormone have not been investigated in humans, as both reported impotency in animals; the follicle-stimulating hormone has been shown to cause oligospermia; zona pellucida has also not been studied in humans as it causes irreversible oophoritis, while the sperm has the potential for success in humans based on the data from immunoreproductive studies. Even as the position of the human chorionic gonadotropin vaccine looks hopeful, research on other possible targets continue with an eventual aim of discovering a vaccine that is more immunogenically effective.

Immunocontraceptives: new approaches to fertility control

The rapidly increasing global population has bowed the attention of family planning and associated reproductive health programmes in the direction of providing a safe and reliable method which can be used to limit family size. The world population is estimated to exceed a phenomenal 10 billion by the year 2050 A.D., thus presenting a real jeopardy of overpopulation with severe implications for the future. Despite the availability of contraceptive methods, there are over one million elective abortions globally each year due to unintended pregnancies, having devastating impact on reproductive health of women worldwide. This highlights the need for the development of newer and improved contraceptive methods. A novel contraceptive approach that is gaining substantial attention is "immunocontraception" targeting gamete production, gamete outcome, or gamete function. Amongst these, use of sperm antigens (gamete function) seems to be an exciting and feasible approach. However, the variability of immune response and time lag to attain titer among vaccinated individuals after active immunization has highlighted the potential relevance of preformed antibodies in this league. This review is an attempt to analyze the current status and progress of immunocontraceptive approaches with respect to their establishment as a future fertility control agent.

Human sperm tail proteome suggests new endogenous metabolic pathways

Proteomic studies are contributing greatly to our understanding of the sperm cell, and more detailed descriptions are expected to clarify additional cellular and molecular sperm attributes. The aim of this study was to characterize the subcellular proteome of the human sperm tail and, hopefully, identify less concentrated proteins (not found in whole cell proteome studies). Specifically, we were interested in characterizing the sperm metabolic proteome and gaining new insights into the sperm metabolism issue. Sperm were isolated from normozoospermic semen samples and depleted of any contaminating leukocytes. Tail fractions were obtained by means of sonication followed by sucrose-gradient ultracentrifugation, and their purity was confirmed via various techniques. Liquid chromatography and tandem mass spectrometry of isolated sperm tail peptides resulted in the identification of 1049 proteins, more than half of which had not been previously described in human sperm. The categorization of proteins according to their function revealed two main groups: proteins related to metabolism and energy production (26%), and proteins related to sperm tail structure and motility (11%). Interestingly, a great proportion of the metabolic proteome (24%) comprised enzymes involved in lipid metabolism, including enzymes for mitochondrial beta-oxidation. Unexpectedly, we also identified various peroxisomal proteins, some of which are known to be involved in the oxidation of very long chain fatty acids. Analysis of our data using Reactome suggests that both mitochondrial and peroxisomal pathways might indeed be active in sperm, and that the use of fatty acids as fuel might be more preponderant than previously thought. In addition, incubation of sperm with the fatty acid oxidation inhibitor etomoxir resulted in a significant decrease in sperm motility. Contradicting a common concept in the literature, we suggest that the male gamete might have the capacity to obtain energy from endogenous pools, and thus to adapt to putative exogenous fluctuations.

Antisperm contraceptive vaccines: where we are and where we are going?

This is a review of current status and future perspectives on the development of antisperm contraceptive vaccines (CV) and immunocontraceptives. The development of antisperm CV is an exciting proposition. There is a strong rationale and recent data indicating that this proposition can translate into reality. The search for novel sperm-specific antigens/genes, that can be used for CV, continues using various recent developing technologies. Various approaches of proteomics, genomics, reproductive biology, mucosal immunity and vaccinology and several novel technologies such as gene knockout technology, phage display technology, antibody engineering, differential display technique, subtractive hybridization, and hybridoma technology are being used to delineate sperm-specific antigens and construct CV. Various sperm antigens/genes have been delineated, cloned, and sequenced from various laboratories. Vaccination with these sperm antigens (recombinant/synthetic peptide/DNA) causes a reversible contraceptive effect in females and males of various animal species, by inducing a systemic and local antisperm antibody response. The efficacy is enhanced by combination vaccination, including peptides based on various sperm antigens. Several human novel scFv antibodies with unique complementarity-determining regions (CDRs), that react with specific well-defined fertility-related sperm antigens, have been synthesized. These human infertility-related antibodies may find application in the development of novel immunocontraceptives. Besides finding the novel sperm antigens, the present and future focus is on enhancing the immunogenicity, bioefficacy, and on obliterating the inter-individual variability of the immune response, and proceeding for primate and human clinical trials. Multi-epitope vaccines combining sperm proteins involved in various steps of fertilization cascade have been found to enhance the immunogenicity and bioefficacy of the contraceptive effect. The in vitro synthesis of infertility-related human scFv antibodies may provide unique once-a-month immunocontraceptives, the first of its kind, for human use. The multi-epitope CV and preformed engineered human antibodies of defined specificity may obliterate the concern related to inter-individual variability of the immune response.

In vitro and in vivo studies evaluating recombinant plasmid pCXN2-mIzumo as a potential immunocontraceptive antigen

PROBLEMS

Study on feasibility of pCXN2-mIzumo as a potential immunocontraceptive antigen.

METHOD OF STUDY

Two groups of mice received 100 microg/mouse plasmids of pCXN2-mIzumo and pCXN2 respectively. RT-PCR Immunofluorescence assay and ELISA were performed to observe pCXN2-mIzumo expression and antibody response in the inoculated mice. Sperm penetration assay and animal mating were employed to detect differences of in vitro fertilization (IVF) rate and mean litter size between the experimental and control groups.

RESULTS

Izumo cDNA positive bands were detected in sample from mice immunized with pCXN2-mIzumo. IgG response started to rise at 2 weeks after first boost and reached the highest antibody titers at 2 weeks after third boost of immunization with pCXN2-mIzumo in the experimental mice. In vitro fertilization rate in the experimental group (11.57%) was significantly lower than that in control (36.60%). Significant difference of mean litter size between female experimental and control groups was observed, and there was significant negative correlation between individual anti-serum titers and litter size (r = -0.308, P < 0.05).

CONCLUSION

pCXN2-mIzumo plasmid possesses appreciable anti-fertility potential.

Experimental immunological infertility effect of anti-GAPDH-2 antibodies on the fertility of female mice

OBJECTIVE

To examine the relationship between an antibody against GAPDH-2, a sperm-specific protein, and infertility of female mice.

DESIGN

Basic research.

SETTING

National Research Institute for Family Planning Beijing, World Health Organization Collaboration Center of Human Reproduction.

ANIMAL(S)

New Zealand rabbit, NIH and ICR mice.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Enzyme-linked immunoabsorbent assay, Western blot and indirect immunostaining assays, standard fertility assay, and sperm agglutination assay.

RESULT(S)

Antibodies against the full-length GAPDH-2 were raised. Its specificity was assessed by immunoblotting and indirect immunostaining assays. The antibody immunoreacted with human sperm GAPDH-2 and the mouse homolog GAPDS but did not cross-react with GAPDH. Treatment of female mice with IP injection of anti-GAPDH-2 serum significantly reduced their fertility. Anti-GAPDH-2 serum caused the agglutination of normal mice sperm in vitro. The anti-GAPDH-2 antibody was detectable in the sera and uterine fluid of the mice immunized with GAPDH-2.

CONCLUSION(S)

These results show that GAPDH-2 should be further evaluated as a promising candidate in the development of an antifertility immunogen. Detecting anti-GAPDH-2 antibodies in the bodily fluid of subjects afflicted with indeterminate infertility may be a new diagnostic index.

Investigation of recombinant mouse sperm protein izumo as a potential immunocontraceptive antigen

PROBLEM

To determine if the recombinant mouse Izumo (mIzumo) could be used as a potential immunocontraceptive antigen.

METHOD OF STUDY

The recombinant mIzumo fused with 6His tag (6His-mIzumo) was purified by immobilized Ni2+ affinity chromatography. Enzyme-linked immunosorbent assay and Western blot were used to detect anti-6His-mIzumo activities of serum from the mice immunized with 6His-mIzumo. Inhibition of the anti-6His-mIzumo antibody on mouse sperm-egg fusion in vitro was performed using the zona free oocytes and acrosome reacted sperm. Fertility of the 6His-mIzumo immunized male and female mice was compared with control mice.

RESULTS

The recombinant mIzumo was successfully produced. Female and male mice inoculated with 6His-mIzumo developed a specific serum antibody and the highest antibody titer lasted at least 6 weeks. The serum anti-6His-mIzumo antibody almost completely blocked mouse sperm-egg fusion in vitro. However, there was no significant reduction in fertility for both male and female mice immunized with 6His-mIzumo compared with control mice.

CONCLUSION

The circulated anti-mIzumo antibody can block mouse sperm-egg fusion in vitro but has no effect on fertility in vivo. It seems that application of Izumo as a candidate antigen in development of contraceptive vaccine needs further investigation.

Effect of sperm DNA vaccine on fertility of female mice

Our laboratory has identified a sperm-specific dodecamer peptide sequence, designated as YLP(12), vaccination with which causes a long-term reversible immunocontraceptive effect in female mice. In the present study, the effects of YLP(12) DNA vaccine were examined. YLP(12) 36 bp cDNA was cloned into pVAX1 vector to prepare the DNA vaccine. Two additional vaccine constructs were made by in frame cloning of one and two CpG repeats in the YLP(12)-cDNA vaccine. Five groups of female mice were immunized intradermally by using gene gun with YLP(12)-cDNA, YLP(12)-cDNA-CpG, YLP(12)-cDNA-CpG-CpG, YLP(12)-cDNA mixed with exogenous synthetic CpG oligodeoxynucleotide (ODN), or vector DNA alone, respectively. Vaccination with all three constructs and the YLP(12) vaccine mixed with exogenous ODN raised antibody response both in the sera as well as locally in the vaginal tract. There was no antibody response in the mice injected with the vector alone. In sera, the highest titers were obtained for the IgG class for all constructs and formulation followed by IgA class. In vaginal washings the highest titers were obtained for the IgA class followed by IgG class. Within the IgG class, the titers for the IgG2a subclass were significantly greater than the IgG1 subclass. Immunization with all constructs and formulation caused a significant (P < 0.05 to <0.001) reduction (20-43%) in fertility of female mice. The highest reductions were seen in mice immunized with YLP(12)-cDNA-CpG-CpG (two repeats) (43% reduction) and with the YLP(12) vaccine administered with exogenous CpG ODN (42% reduction). T lymphocytes obtained from DNA-vaccinated mice showed clearly distinguished comparative RT-PCR analysis of cytokine mRNA expression for Th1 and Th2 immune responses compared to T lymphocytes obtained from control animals injected with vector DNA. Expression of both Th1 cytokines (IL-2 and IFN-gamma) and Th2 cytokines (IL-4 and IL-10) was enhanced after DNA vaccination as compared to controls, with a bias towards Th1 response. The immunocontraceptive effects were long-lasting observed up to 1.3 years of the observation period and increased with time. These novel findings indicate that the intradermal immunization with a sperm-specific DNA vaccine causes a long-term circulating and local immune response resulting in immunocontraceptive effects in female mice.

Antisperm Vaccine for Contraception

PROBLEM

This study is a review of antisperm contraceptive vaccine (CV) development with the main focus on research going on in our laboratory.

METHOD OF STUDY

Various methods of proteomics and genomics, hybridoma technology, substractive libraries, differential display method, and phage display technology were used to obtain sperm-specific genes and proteins. The present study will primarily focus on the sequences obtained by using the phage display technology and their role in CV development and human immunoinfertility.

RESULT

Four novel peptides, delineated by using the phage display technology, were found to be involved in human immunoinfertility. The vaccine based on one of these peptides, designated as YLP(12), caused a reversible contraception in female mice.

CONCLUSIONS

The vaccine targeting sperm is a feasible and exciting approach to contraception. The phage display technology is a powerful tool to delineate sperm-specific peptide sequences that can be used for the CV development and in the diagnosis and treatment of infertility mediated through antisperm antibodies.

Are antisperm antibodies indeed sperm-specific?

Antisperm antibodies (ASA) are present in a high percentage of infertile patients. The development of ASA in the male depends on the sequestration of antigens on germ cells, the testis being an immune privileged region. In this study, we investigated the specificity of ASA binding to sperm antigens by exposing a number of organ preparations to ASA. In none of the organ homogenates was a significant difference between the results of the Western blot with ASA-containing fluids, neither serum nor seminal plasma, and those without ASA observed. We conclude from our results that the ASA tested in our study obviously are sperm-specific. ASA as an autoimmune are thus restricted to spermatozoa. The antigens are suitable for trials in immune therapy, they may also serve for the development of antigen-specific diagnosis and treatment in infertility. They also indicate cognate antigens of possible immune contraceptive agents.

Recent advances in contraceptive vaccine development: a mini-review

Contraceptive vaccines (CV) may provide viable and valuable alternatives to the presently available methods of contraception. The molecules that are being explored for CV development either target gamete production [luteinizing hormone-releasing hormone (LHRH)/GnRH, FSH], gamete function [sperm antigens and oocyte zona pellucida (ZP)], and gamete outcome (HCG). CV targeting gamete production have shown varied degrees of efficacy; however, they either affect sex steroids causing impotency and/or show only a partial rather than a complete effect in inhibiting gametogenesis. However, vaccines based on LHRH/GnRH are being developed by several pharmaceutical companies as substitutes for castration of domestic pets, farm and wild animals, and for therapeutic anticancer purposes such as in prostatic hypertrophy and carcinoma. These vaccines may also find applications in clinical situations that require the inhibition of increased secretions of sex steroids, such as in uterine fibroids, polycystic ovary syndrome, endometriosis and precocious puberty. CV targeting molecules involved in gamete function such as sperm antigens and ZP proteins are exciting choices. Sperm constitute the most promising and exciting target for CV. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Studies are focused on delineating appropriate sperm-specific epitopes, and increasing the immunogenicity (specifically in the local genital tract) and efficacy on the vaccines. Anti-sperm antibody (ASA)-mediated immunoinfertility provides a naturally occurring model to indicate how a vaccine might work in humans. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects, but may induce oophoritis, affecting sex steroids. They are being successfully tested to control feral populations of dogs, deer, horses and elephants, and populations of several species of zoo animals. The current research for human applicability is focused on delineating infertility-related epitopes (B-cell epitopes) from oophoritis-inducing epitopes (T-cell epitopes). Vaccines targeting gamete outcome primarily focus on the HCG molecule. The HCG vaccine is the first vaccine to undergo Phase I and II clinical trials in humans. Both efficacy and lack of immunopathology have been reasonably well demonstrated for this vaccine. At the present time, studies are focused on increasing the immunogenicity and efficacy of the birth control vaccine, and examining its clinical applications in various HCG-producing cancers. The present article will focus on the current status of the anti-sperm, anti-ZP, anti-LHRH/GnRH and anti-HCG vaccines.

Contraceptive vaccines

The world's population is growing at a tremendous rate, affecting growth and development. Apart from this population growth, unintended pregnancies resulting in elective abortions continue to be a major public health issue. In over half of these unintended pregnancies, the women have used some type of contraception. Thus, there is an urgent need for a better method of contraception that is acceptable, effective and available. The contraceptive choices available to women at this time include steroid contraceptives, intrauterine devices, barrier methods, spermicides, natural family planning, male and female sterilisation, and recently available emergency contraceptives. Contraceptive vaccines (CVs) may provide viable and valuable alternatives that can fulfill most, if not all, properties of an ideal contraceptive. Since both the developed and most of the developing nations have an infrastructure for mass immunisation, the development of vaccines for contraception is an exciting proposition. The molecules that are being explored for CV development either target gamete production (gonadotropin releasing hormone, follicle-stimulating hormone and luteinising hormone), gamete function (zona pellucida [ZP] proteins and sperm antigens) or gamete outcome (human chorionic gonadotropin [hCG]). Disadvantages of CVs targeting gamete production are that they affect sex steroids and/or show only a partial effect in reducing fertility. CVs targeting gamete function are better choices. Vaccines based on ZP proteins are quite efficacious in producing contraceptive effects. However, they invariably induce oophoritis affecting sex steroids. Sperm antigens constitute the most promising and exciting targets for CVs. Several sperm-specific antigens have been delineated in several laboratories and are being actively explored for CV development. Antisperm antibody-mediated immunoinfertility provides a naturally occurring model to indicate how an antisperm vaccine will work in humans. Vaccines targeting gamete outcome primarily focus on the hCG molecule. The hCG vaccine is the first vaccine to undergo phase I and II clinical trials in humans. Both the efficacy and the lack of immunotoxicity have been reasonably well demonstrated for this vaccine. The present studies focus on increasing the immunogenicity and efficacy of this birth control vaccine.

Identification of sperm immunoreactive antigens for immunocontraceptive purposes: a review

Antisperm antibodies (ASA) may be a reason of infertility in some individuals. They may affect pre- as well as post-fertilization stages of the reproductive process. There is ongoing progress in the identification of sperm antigens related to fertilization. The employed methods for this purpose include recombinant DNA technology and the most advanced proteomic analysis. This paper enlists the different approaches undertaken in order to identify and characterize the immunoreactive sperm antigens. We have mainly focused on those, which have been already studied in regard of their immunocontraceptive potential, although it has been impossible to include all published data concerning the topic in a single article. Few novel sperm auto- and isoantigens, discovered recently, have also been reviewed even if their role in fertilization has not been yet established.

Sperm specific proteins-potential candidate molecules for fertility control

The increase in population growth rate warrants the development of additional contraceptive methods that are widely acceptable, free from side effects and less expensive. Immunocontraception, and in particular the targeting of antibodies to gamete-specific antigens implicated in sperm egg binding and fertilization, offers an attractive approach to control fertility. The development of a contraceptive vaccine based on sperm antigen represents a promising approach to contraception. In mammals, fertilization is completed by the direct interaction of sperm and egg, a process mediated primarily by sperm surface proteins. Sperm have proteins that are unique, cell specific, immunogenic and accessible to antibodies. A few of the sperm specific proteins have been isolated and characterized. The antibodies raised against the sperm specific antigens have proved to be extremely effective at reducing sperm-egg interaction in vitro; fertility trials in sub-human primates would eventually prove the effectiveness of the sperm antigens in terms of contraceptive efficacy.

Novel human prostate-specific cDNA: molecular cloning, expression, and immunobiology of the recombinant protein

The differential display-polymerase chain reaction technique was employed to obtain a prostate-specific approximately 300-bp cDNA fragment. On screening the human prostate-lambdagt10 library with this fragment, a full-length approximately 1.5-kb cDNA encoding for a prostate antigen, designated as human novel prostate-specific antigen (hNPSA), was found. Extensive database searches revealed that the hNPSA cDNA is a novel sequence. It has an open reading frame (ORF) of 735-bp encoding for 245 amino acids (aa), with a calculated molecular mass of approximately 27kDa. Hydrophilicity analysis of the deduced aa sequence indicated that hNPSA is a membrane-anchored peptide. Analysis for tissue-specificity by Northern blot and RT-PCR-Southern blot procedures indicated that hNPSA is specifically expressed only in human prostate. The hNPSA (ORF) was subcloned into pET22b(+) vector and expressed using the histidine-tagged gene fusion system. The recombinant (r) protein of approximately 27kDa was purified and antibodies (Ab) were raised in rabbits. The rhNPSA Ab recognized a specific protein band of approximately 35kDa in solubilized human prostate tissue and not in any of the other 10 human tissues tested in the Western blot procedure. The hNPSA expression is upregulated 2.5- to 3-fold, both at the mRNA and protein levels in androgen-dependent LNCaP cells, as compared to normal whole prostate tissue. Antisense, but not the sense, phosphothiorate-conjugated oligonucleotides based on the hNPSA cDNA sequence significantly (p<0.001) inhibited proliferation of LNCaP cells in a concentration-dependent manner. Thus, the novel hNPSA, which has prostate-specific expression and seems to be involved in carcinogenesis, may have applications in the specific diagnosis and treatment of prostate cancer.

Effect of antibodies to sperm-specific recombinant contraceptive vaccinogen (rCV) on murine fertilization: search for an animal model to examine its contraceptive potential

Recently, we cloned and sequenced a sperm-specific antigen, designated as Contraceptive Vaccinogen (rCV), from human testis (Naz et al., 2001). The present study was conducted to examine its proteomic homologue and function in murine sperm, in order to find out whether or not the mouse can provide a suitable model for examining its immunocontraceptive effects. This was examined by using purified antibodies (Ab) raised against the recombinant (r) human CV antigen of approximately 44 kD. In the Western blot procedure, rCV antibodies recognized a specific protein band of approximately 64 +/- 5 kD in murine testis and murine sperm extracts, the band similar to that found in human testis and human sperm. In the immunoprecipitation procedure, rCV Ab immunoprecipitated a protein band of similar size from murine sperm and murine testis extracts. The immunocytochemical (ICT), immunoscanning electronmicroscopic (ISEM) and the immunobead binding technique (IBT) revealed the subcellular localization of CV antigen on the surface of acrosome and tail regions of the noncapacitated and capacitated murine sperm cell. In functional bioassays, rCV Ab inhibited the acrosome reaction as well as sperm-egg binding in vitro. These data indicate that the CV antigen is expressed in murine sperm and has a biological role in sperm function and sperm-egg binding. In vitro inhibition of capacitation/acrosome reaction and sperm-zona binding suggest that the mouse can provide a suitable model to examine the immunocontraceptive effects of CV antigen in actively-immunized animals.